The objective of this project is to explore and develop new means of controlling caries by investigating methods of interfering with the transport of mineral out of tooth structure. Polymer or polymer-forming formulations are to be deposited inside early, subsurface, lesions. The polymer systems to be investigated are those which can be expected to operate as diffusion barriers and/or by releasing fluoride into the local lesion environment. Several polymer systems have been studied: phenol/aldehydes, the fluoride salts of amine-substituted monomers, phosphonate-substituted monomers, hydroxyl-substituted monomers, and preformed polymers with phosphonate and/or fluoride-releasing pendant groups. The fluoride salts of several amine-substituted monomers were found to be capable of rapid homo- and copolymerization at mouth temperature in bulk, and in aqueous and alcoholic solutions. The most promising of these materials fully permeates subsurface enamel lesions when applied with a brush, and polymerizes in 10-15 min as a highly crosslinked terpolymer. Untreated lesions were found to release 3 times the amount of phosphate in weak acid buffer as did lesions treated with the terpolymer. It releases a total of 8 mg fluoride/g at a decreasing rate over four days in neutral buffer, during which time it adsorbs only 4 percent by weight of water. A preformed polymer containing phosphonate pendant groups was found to have a strong adsorption affinity for hydroxyapatite. This polymer forms a protective film when applied from 50 percent ethanol. A monomolecular layer provides substantial protection against weak acid demineralization. Such a material could serve as a protective mouthrinse.